An internal combustion engine may include both a main chamber and a pre-chamber or antechamber. The main chamber includes a piston configured to reciprocate during a combustion cycle. The pre-chamber is positioned above the main chamber and within the cylinder head of the engine. The pre-chamber may include a spark plug such that combustion may be initiated in the pre-chamber rather than the main chamber. Because there is lower turbulence of the air and/or fuel within the pre-chamber relative to the main chamber at the time of ignition, initiating combustion in the pre-chamber, rather than the main chamber, may allow for consistent initial flame kernel growth which may lead to more efficient combustion.
Various types of pre-chambers may be provided within the cylinder head, including a passive pre-chamber and a fuel-fed pre-chamber. A passive pre-chamber assembly does not directly receive any air and/or fuel, but rather, receives air and/or fuel from the main chamber during the compression stroke of the piston. However, the charge within a passive pre-chamber is leaner (i.e., includes less fuel content) than the charge in the main chamber because the charge within the passive pre-chamber assembly includes both new or fresh charge pumped into the pre-chamber assembly from the main chamber and residual charge that has remained within the main chamber after a previous combustion cycle. As such, the residual charge dilutes the new charge which decreases the fuel content present in the passive pre-chamber. The leaner charge within the passive pre-chamber assembly may require more ignition energy to combust and/or may have an elevated temperature which can increase the tendency of the charge to pre-ignite.
Additionally, a fuel-fed pre-chamber, rather than a passive pre-chamber, may be included on an engine. The fuel-fed pre-chamber directly receives raw fuel during a combustion cycle. The fuel-fed pre-chamber may require an external compressor to pump fuel to the pre-chamber. As such, additional components may be necessary to operate an engine with a fuel-fed pre-chamber, and the cost of the compressor, the associated control unit, and maintenance of the pre-chamber and its additional components may be prohibitive for certain engines or applications.